1. Field of the Invention
The present invention relates to an ironing apparatus. More particularly, the invention relates to an ironing apparatus for ironing a plate-like work.
2. Description of Related Art
There is a demand for changing plate thickness of a part of a panel member making up a vehicle body to achieve weight reduction while assuring a safety performance of an automobile. Therefore, the use of a high tensile steel plate having high strength is considered. However, since the high tensile steel plate is expensive, the cost of materials increases. Further, it is difficult to employ the high tensile steel plate having certain quality, because the costs greatly increase depending on the places, due to regional differences in the supply system.
Thus, the use of a tailored blank has been proposed. This tailored blank is formed by welding a plurality of kinds of plates having different plate thicknesses.
However, if employing this method, an equipment for joining the plates is required and increases the costs. Also, at a junction of materials, the strength is lowered, or the formability is worse, there is a problem that the structure of a forming die is complicated.
Also, the ironing process has been proposed. The ironing process is, by ironing part of a plate material having certain thickness with a tool, to make thinning the ironed part of the plate material.
Japanese Patent Unexamined Publication JP-A-2006-297461 proposes an ironing method using a press machine. In the press machine of the proposed ironing method, a position of an upper die is horizontally shifted from a position of a lower die from a distance D which is smaller than a thickness of a work. The work is placed between the upper and lower dies, the upper and lower dies are vertically moved to approaches each other so as to pinch the work therebetween, and then, the work is ironed so that the thickness of the pinched portion of the work becomes the distance D which is smaller than the initial thickness of work.
According to this method, there is no junction, unlike the tailored blank, and the lowering strength at the junction can be prevented.
However, in this method, when vertically moving the upper and lower dies while pinching the work therebetween, each die is subjected to a reaction force in the horizontal direction. Therefore, it was required to increase the rigidity of the entire press machine, and thus, the apparatus becomes large in size.